1. Field of the Invention
The present invention relates to an ink jet printing apparatus. Particularly, the present invention relates to a method of performing a process for maintaining a color ink jet printing head capable of making a print with multiple color inks for the purpose of keeping the color ink jet printing head capable of ejecting the inks stably.
2. Description of the Related Art
Ink jet printing apparatuses eject liquids such as inks to a printing medium from their ink jet printing heads depending on inputted image data, and thus print multiple dots on a printing medium, thereby forming the image thereon. A common practice for ink jet printing apparatuses each with such a configuration is that a maintenance process (hereinafter also referred to as a “recovery operation”) is applied to their printing heads for the purpose of keeping their ink ejecting conditions adequate.
The maintenance process consists of a suction recovery process, a preliminary ejection process, a wiping process and the like. The suction recovery process is that which discharges inks from individual ejection openings forcedly by generating a negative pressure inside a cap by use of pumping means such as a tube pump and a piston pump while a face of a printing head, in which the ejection openings are arranged, is covered with the cap. This suction recovery process makes it possible to remove thickened inks and bubbles in printing head ink chambers, which adversely affect its ejection operation, from the interior of the head.
In the preliminary ejection process, an ejection operation is preliminarily carried out in order for inks to be stably ejected from the individual ejection openings. Particularly, in a case of a printing head which has just undergone the suction recovery process, it is likely that part of inks once discharged into the cap by the forced suction may flow back to the insides of the individual ejection openings. In other words, part of the thickened inks returns to the insides of the ink chamber and the nozzles in the printing head. In a case where the face in the printing head which ejects multiple color inks is configured to be covered with a single cap, ink mixed up by multiple color inks in the cap flows back into the insides of nozzles assigned for the respective color inks. With these problems taken into consideration, a common practice performed after carrying out the suction recovery process is to preliminarily eject multiple color inks from the individual ejection opening toward the inside of the cap while the inside of the cap is caused to communicates with the atmosphere for the purpose of discharging the thickened inks and the mixed ink. For example, the preliminary ejection is carried out approximately 20000 times with an ejection frequency of 10 kHz for each nozzle assigned for a corresponding one of the multiple color inks. It does not matter how many times the preliminary ejection should be carried out with what driving frequency, as long as the number of times and the frequency are enough for discharging the thickened inks and the mixed ink which flow back into the individual nozzles.
The wiping process is that to be carried out for the purpose of wiping inks, which adhere to the surface of the printing head in conjunction with the suction recovery process, the preliminary process and regular printing operations, off the surface by use of a wiping member.
As described above, as long as the suction recovery process, the preliminary ejection process and the wiping process are carried out at adequate timings before, during and after each printing operation, it is possible to keep the ejecting operation of the printing head in a stable condition.
Inks are consumed for the suction recovery process and the preliminary ejection process, which have been described above, regardless of actual printing operations. For the purpose of cutting back on running costs, it is desirable that amounts of inks consumed for these processes should be held as small as possible. In particular, large amounts of inks are often suctioned for the suction recovery process to be carried out when replacing old ink tanks with new ones from a viewpoint of stabilizing the ejecting operation. A key point for cutting back on running costs is to hold the amounts of suctioned inks and the amounts of preliminarily ejected inks as small as possible.
Japanese Patent Laid-Open No. 07-17058 (1995) discloses a method of making amounts of suctioned inks different between the suction recovery process to be carried out for ink tank replacement and the suction recovery process to be carried out for the purpose of doing things other than the ink tank replacement. In addition, Japanese Patent Laid-Open No. 2003-291368 discloses a process for avoiding carrying out the suctioning operation both before and after ink tank replacement. Furthermore, Japanese Patent Laid-Open No. 2005-306013 discloses a method of making an amount of suctioned ink different according to ink type (ink color) in an ink jet printing apparatus which simultaneously applies a suction recovery process to a printing head for ejecting multiple color inks by use of a single cap. Moreover, Japanese Patent Laid-Open No. 2004-98626 discloses an effective preliminary ejecting method to be carried out after a suction recovery process of an ink jet printing head which has a nozzle row for printing larger dots and a nozzle row for printing smaller dots for each type of ink.
After gradually decreasing inks in the respective ink tanks depending on use, the ink jet printing apparatus finally becomes capable of carrying out no printing operation. For the purpose of avoiding a situation in which a printing operation can be carried out no longer suddenly in the middle of making a print on a sheet of paper, many of ink jet printing apparatuses of a regular type include means for estimating amounts of remaining inks on a basis of how many times the printing head has ejected and been suctioned, and inform their users that an ink remains in a very small amount when the amount of the remaining ink becomes very small, thus urging the users to replace the old tank with a new one. However, the old ink tank is not necessarily replaced with the new one immediately when their users are informed that the amount of the remaining ink is very small. Even though the users are informed that the amount of the remaining ink is very small, they are likely to continue the printing operation for a while, in a case where the number of sheets of paper on which a print remains yet to be made is very small, or in a case where no new ink tank with which the old ink tank is replaced is on hand.
In this respect, let us discuss how the pressure inside an ink tank changes after the ink tank becomes nearly empty of its ink. First of all, in a case of an ink tank whose inside can communicate with the atmosphere, as the ink in the ink tank is discharged therefrom in conjunction with an ejection operation, the air is suctioned into the ink tank, and an air path is thus formed in the ink tank. In other words, the inside of the ink tank can maintain an atmospheric pressure equal to that of the external air. On the other hand, in a case of an air-tight ink tank whose inside can not communicate with the atmosphere, the negative pressure in the tank increases rapidly after an amount of ink remaining in the tank becomes very small. Subsequently, when the value representing the negative pressure goes beyond the meniscus pressure (that is, a pressure which ink in the vicinity of a nozzle in a printing head can withstand for forming a meniscus due to mutual attraction between the capillary force of the nozzle and the negative pressure in the ink tank), the ink starts to flow back. In recent years, not only atmosphere-communicating ink tanks each containing an ink in an absorber such as a sponge but also air-tight ink tanks each are capable of containing an ink in the form of a liquid are supplied in.
In the case of an air-tight ink tank, once inks flow back as described above when a suction recovery process is carried out, mixed ink, which has been present in the cap, flows into the individual nozzles, and is thus introduced to the insides of the common ink chamber and ink supplying ports in the printing head, and as far as to the insides of the ink tanks. Furthermore, if old ink tanks are replaced with new ones while the mixed ink remains in the insides of the common ink chamber, ink supplying ports and the like, it is likely that part of the mixed ink remaining in vicinities of the ink supplying ports with which to connect the printing head and the ink tank may likely enter the new ink tank with which the old ones are replaced.